Input detection methods in a capacitive touch input device that detects an input position inputted by an input operator such as a finger are classified into a self-capacitance method (single-line method) and a mutual capacitance method (two-line method). According to the self-capacitance method, a detection electrode whose stray capacitance has been increased as a result of the approach of an input operator is detected and the input position is detected on the basis of the arrangement position of the detection electrode. According to the mutual capacitance method, a detection voltage at a predetermined voltage level is applied to drive electrodes. Then, a detection electrode whose detection voltage level has been decreased as a result of the approach of an input operator is detected, and the input position is detected on the basis of the arrangement position of the detection electrode. The former method has a simple configuration due to the absence of the wiring of drive electrodes. In the former method, however, the stray capacitance to be detected is at a very small level from 10 to 20 pF, i.e., the level difficult to be detected. Thus, the latter mutual capacitance method is generally employed.
The mutual capacitance method is further classified into a projective method and a cross-point method. According to the projective method, a plurality of X-direction electrodes and a plurality of Y-direction electrodes are arranged on an insulation panel so as to be insulated from each other. A detection operation using one of the X-direction electrodes and the Y-direction electrodes as drive electrodes to which a detection voltage is applied and using the other one of those electrodes as detection electrodes for detecting detection voltage levels and a detection operation using the other as drive electrodes and the one as detection electrodes are performed in an alternate manner. Based on the position of the detection electrode whose detection voltage level has been decreased, the input position in the X and Y directions is detected. According to the cross-point method, a plurality of drive electrodes to which a detection voltage is applied and a plurality of detection electrodes for detecting detection voltage levels are arranged so as to be perpendicular to each other. From among intersections between the drive electrodes and the detection electrodes, the input position is detected on the basis of the intersection of the detection electrode whose detection voltage level has been decreased. According to the projective method, a detection voltage is applied simultaneously to all of the plurality of drive electrodes which are one of the X-direction electrodes and the Y-direction electrodes. The detection electrode whose detection voltage level has been decreased is detected from among all of the detection electrodes which are the other one of the X-direction electrodes and the Y-direction electrodes. Thus, the input position can be detected within a short period of time. However, when input operations are simultaneously made on two different input positions on an input operation surface, virtual images determined as two input positions are additionally generated in the X and Y directions of the two input positions. Thus, the input positions cannot be detected for the case of the simultaneous input operations made on two or more points in the projective method.
According to the cross-point method, on the other hand, a detection voltage level obtained as a result of the approach of an input operator is detected for all of the intersections. Thus, even if input operations are simultaneously made on two or more different positions, each such an input position can be detected. However, the detection of the input positions takes long since a detection voltage is applied for each of pluralities of drive electrodes and detection voltage levels are detected for all of the detection electrodes intersecting with that drive electrode group with the detection voltage applied thereto. In a capacitive touch panel with an enlarged input operation surface, in particular, the number of intersections to be detected is proportionally increased. Thus, reduction in the response speed of an input operation becomes apparent.
In view of the above, according to the related capacitive touch panel that detects an input position with the cross-point method, capacitive touch panels such as Patent Literatures 1 and 2 have been proposed. According to the capacitive touch panel in Patent Literature 1, interlaced drive scanning is performed in which part of drive electrodes with a detection voltage applied thereto is skipped. Upon the detection of an input operation, drive scanning is performed in detail for all of the drive electrodes in the vicinity of the input position. According to the capacitive touch panel in Patent Literature 2, a plurality of drive electrodes adjacent to each other in the drive scanning direction are bundled and a detection voltage is applied to each bundled drive electrode group.
FIG. 6 is an explanatory diagram for illustrating a method for detecting an input position in a capacitive touch panel 100 disclosed in Patent Literature 2. According to the capacitive touch panel 100, from among a plurality of drive electrodes Dn (n is a natural number greater than or equal to 1) arranged in a direction perpendicular to the plane of paper in the figure, two drive electrodes D2n-1 and D2n adjacent to each other in a drive scanning direction (the horizontal direction in the figure) are grouped together as a drive electrode group. An AC drive voltage is then applied to each drive electrode group DV(n). Each of graphs (a), (b) and (c) of FIG. 6 shows a relationship, when the drive voltage is applied to the drive electrode group DV(n), between an input position of an input operator along the drive scanning direction and a detection voltage level R(m,n) appearing at a detection electrode S(m) arranged along the drive scanning direction in the vicinity of the input position with the polarity of the detection voltage level R(m,n) inverted.
As is apparent from FIG. 6, when the input operator comes close to the vicinity of the drive electrode group DV(n) with the drive voltage applied thereto, the capacitance between the drive electrode with the drive voltage applied thereto and the input operator is increased. Part of the drive voltage signal is flown into the input operator and the detection voltage level R(m,n), which detects the drive voltage, is decreased (increased in FIG. 6 due to the inverted polarity) in the detection electrode capacitively-coupled with the drive electrode at a certain capacitance. When the input operator is positioned at a place distant from the drive electrode group DV(n) with the drive voltage applied thereto, on the other hand, the capacitance between the drive electrode with the drive voltage applied thereto and the input operator is decreased to a negligibly small level in comparison to the capacitance between that drive electrode and the detection electrode. Thus, the detection voltage level R(m,n) detected in the detection electrode does not change.
Thus, based on the detection voltage levels R(m,n) appearing at the detection electrode S(m) when the drive voltage is applied to the drive electrode groups DV(n), the input position of the input operator can be detected. For example, assuming that the input position is at y0 in the figure along the drive scanning direction, when the drive voltage is applied to the drive electrode groups DV(n) (n is from 1 to 3), the detection voltage levels R(m,n) detected from the detection electrode S(m) are a0, b0, and c0, respectively, in accordance with the respective amounts of change. The detection voltage level R(m,n) gets smaller at a greater distance from the wiring position of the drive electrode group DV(n) with the drive voltage applied thereto. Thus, the input position y0 between the wiring positions of the drive electrode group DV(1) and the drive electrode group DV(2) is obtained from the ratio between a0 and b0.
In this manner, according to the related capacitive touch input devices described in Patent Literatures 1 and 2, the number of drive voltage applications is smaller than the number of detection electrodes actually wired. Thus, an amount of time taken for detecting an input position can be shortened.